The proposed research will chart the course of deterioration of various aspects of written language processing in patients with probable Alzheimer's Disease (AD). Although oral and written language disturbances are well-recognized symptoms of AD, there are disagreements about the cognitive mechanisms underlying these deficits and about the manner in which the deficits evolve over the disease course. Resolution of these disagreements is important for characterizing the clinical symptoms of AD more accurately so that this information ca be used in the differential diagnosis of AD with respect to other types of neurological illnesses and planning behavioral interventions for patients and caregivers. Detailed investigations of the language processing deficits in AD can also contribute to refining neurolinguistic models of normal language functions by testing hypotheses generated by competing cognitive theories. Newly developed measures of written language dysfunction may be used to quantify the severity of cognitive impairments through the full course of AD (not just mild dementia) and monitor effects of therapeutic interventions on cognitive functions. Patients with probable AD will be followed longitudinally to assess how various aspects of orthographic, phonological and semantic lexical processing become impaired over the disease course. Healthy controls will be tested first to develop standardized reading and spelling tests. Oral reading, spelling to dictation and repetition of words and pseudowords then will be assessed serially in AD patients over six testings, each six months apart. A new lexical priming procedure, threshold oral reading, will be used to evaluate longitudinally the dissolution of different types of knowledge in semantic memory. AD patients and healthy controls will be examined on two occasions, one year apart, to assess effects of priming nonsemantic lexical-associative and various types of semantic-conceptual relationships. Both group statistics and individual case analyses will be used.